texts: Galactic winds/outflows: why and how are they detected via blueshifted absorption lines in spectra?

texts: I know that galaxies can eject gas due to supernovae, accreting black holes, etc. These galactic "winds/outflows" are often defined/detected observationally using blueshifted absorption lines in spectra. But why is it always blueshifted absorption -- what about redshifted absorption? Does it have something to do with the outflow velocities being measured relative to the galaxy central/systemic velocity, such that redshifted absorption implies inflow instead of outflow? But what's the geometrical picture?


texts: Why Earth's perihelion occurs 3rd January rather than 1st?

texts: Why Earth's perihelion occurs 3rd January rather than 1st January? Is there any effort to correct this discrepancy?


texts: A blue moon is two full moons in the same month.  How many times will a blue moon occur in the average lifetime of say 70 years?


texts: What implications does younger volcanism have on the Moon's thermal evolution?

texts:
In the paper Evidence for basaltic volcanism on the Moon within the past 100 million years (Braden et al. 2014), suggest that features such as Ina (image below) represent a far more recent age of volcanism (relatively speaking, around 100 million years).

Image source: NASA Science News, where they have a different non-volcanic theory.  However, this question is not about whether the features are volcanic or not.

From the Braden et al. article abstract:

  The morphology of the features is also consistent with small basaltic eruptions that occurred significantly after the established cessation of lunar mare basaltic volcanism. Such late-stage eruptions suggest a long decline of lunar volcanism and constrain models of the Moon’s thermal evolution.

Assuming the latest models indicate volcanism as recent as within the 100 million years ago, what are the implications for lunar thermal history of younger volcanism?


texts: How do astronomers distinguish the spectral lines?

texts: As a black body a star emits a continuous spectrum of light and other radiation. I've learned they are capable of knowing of what elements the stars are made of because of the spectral lines. But how do they distinguish those lines from other radiations?


texts: Astronomical animations of deep space objects

texts:
Is there any real animations from NASA or others (not simulation or Artist's impression) like this

https://svs.gsfc.nasa.gov/vis/a000000/a004400/a004442/frames/730x730_1x1_30p/

or this

https://svs.gsfc.nasa.gov/vis/a000000/a004000/a004038/frames/4096x4096_1x1_30p/304A-Frames/

for deep space objects like galaxies, nebula, Binary star, etc?

Or it is really not possible to get animation, because it is too far and everything is looks very slow from earth?

Because whatever I found so far is only solar system animations (planets, moon, Sun, etc), software simulation or Artist's impression.


texts: Throwing a baseball from orbit to the earth

texts:
I just read a thought piece about what a war in space may look like, and it changed my thoughts on what orbit actually is. From what I read about orbits, it sounds like going faster in the velocity direction will cause you to get to a lower altitude, and going slower will cause you to get to a higher altitude orbit. This feels completely backwards to me, so I tried a thought experiment, but it led me to the questions below.
I'm standing on satellite in a circular low earth orbit, and I want to make my (indestructible) baseball go to the ground without waiting for months or years to de-orbit. If I threw the baseball in the velocity direction, I don't think I could cause enough delta V to make it go fast enough that it would go to a significantly lower orbit. Is that correct?
So instead of throwing it in the velocity direction, if I threw it straight at the earth (nadir), would it continue to go towards the earth, or would that just modify the baseball's orbit similar to throwing it in the velocity direction? I remember hearing about something "bouncing off the atmosphere". That wouldn't come into play with my baseball would it?
If I threw the baseball in the wake direction to try to take a bit of my orbital speed off of it, would it truly get to a higher orbit? Why wouldn't it just fall to the ground?
Bonus question: if I threw it anti-nadir, what happens?


texts:
So, I've googled and wiki'd on this, but no clue, so I turn my question to the community:

Given Titan's nice orange haze that is supposedly composed of Tholins and strangely coincides with its stratosphere (taken from wikipedia)

I got to think whether the haze takes the role of clouds on earth when it comes to energetics. From this a bunch of questions arose:

Do we know whether the haze is responsible for heat trapping and thus, the formation of a stratosphere on Titan?
What about radiation transport modelling with those particles, is this successful?
Also I'd be interested in what we know about the stability of Tholins. Could they survive harsh irradiation that atmospheres on Hot Jupiters do encounter?

I would like to be able to make a statement such as "Dust" or "Haze-controlled" energetics for the stratosphere of Titan, if this is so. It would be nice if you helped to clear this up.


texts: I recently saw this video. The creator of the video says that one of the reasons for non-existence of life on planets around red dwarfs might be that these stars can increase luminosity roughly by a factor of 2 in a matter of seconds which will boil off water from planets. He also said something about Helium/Hydrogen convection belts which are responsible for this. Can someone please explain this phenomenon?


texts:
This answer to Did comets 266P/Christensen or P/2008 Y2 (Gibbs) cause the Wow! signal? points out that the comets in question were nowhere near where the radio telescope was pointed.

Wikipedia says that the Ohio State University Radio Observatory (or Big Ear) was a Kraus-type radio telescope but doesn't provide enough information to deduce a field of view.

Questions:

What was the field of view of the Ohio State University Radio Observatory of Wow! signal fame?
What would be the typical rise and fall times of a steady source passing through the fixed telescope's field of view as the Earth rotated?


texts: How to determine the temperature of a star according to the strength of the line in the spectra?

texts:
Based on the comments, I have changed some things.
Below is a graph showing the relative strength of $H_\gamma$ and Fe I lines of two stars. Which star is hotter?

This is a question from the book:An Introduction to
Stellar Astrophysics(2010).Francis Leblanc.
The full question is shown below.

And also, some of my ideas:

As for Fe I, based on Saha equation, we can calculate as follows:
$\frac{n_{\mathrm{II}}}{n_{\mathrm{I}}}=\frac{1}{n_{\mathrm{e}}}\left(\frac{2 \pi m_{\mathrm{e}} k T}{h^{2}}\right)^{\frac{3}{2}} \frac{2 U_{\mathrm{II}}}{U_{\mathrm{I}}} \mathrm{e}^{-\frac{E_{\mathrm{ion}}}{k T}}$, suppose here $n_e$ is a constant.$U_{II}   $ and $U_{I}$ are the partition function for Fe II and Fe I respectively, which are also constants. $E_i   $ is the energy required to ionize one electron, which is obviously a constant. So as T increase, $\frac{n_{II}}{n_{I}}$ will increase. Because, it is relatively harder for ionize one more electron. So almost all of the Fe element are $Fe I$ or $Fe II$. Tues the strength of spectra line of $FeI $ will decrease as temperature increases. So star A is hotter.
As for $H_{\gamma}$, I have no idea about that. Although I can use Bolzmann equation to find relative number density of different state of hydrogen. But there are serval states. n=3 ,n=4, n=5.


texts: Can a change in the density of interstellar and intergalactic quantum fields affect the Redshift of photons?

texts:
Using our solar system's heliosphere as an analagy to what is happening in our galaxy and even the universe as a whole, can light redshift with changes in quantum fields?

The universe is constantly being bombarded by particles from stars, pulsars, quasars, black holes, etc..    Is it possible for these particles to interact with photons in a way that will cause light to redshift?


texts: Why do these Hubble images of Neptune look like Cheela?

texts:
The open access paper Formation of a New Great Dark Spot on Neptune in 2018 (cited in Gizmodo's Formation of Dark Vortex on Neptune Captured For the Very First Time and Phys.org's Hubble captures birth of giant storm on Neptune) shows images of Neptune taken by the Hubble Space Telescope.

The projections are called "global cylindrical maps" and those usually result in weirdly stretched features near the poles but do not result in the spiky hairdo or Cheela-like appearance in the Hubble  images below.

Source

What causes this effect seen in these projections?

  Individual maps from Hubble images in 2017 through 2018, in the same filters and processing as Figure 1. These maps span ±90° of latitude and longitude, and tick marks indicate 30° latitude and longitude intervals.

  False‐color global cylindrical maps from Hubble, spanning 180° of latitude and 360° of longitude, from images at 845 (red), 547 (green), and 467 nm (blue), and all use the same contrast scaling with a light unsharp mask applied. The maps are centered on 180°W longitude, except 2015, which was centered on 0° longitude. Dotted lines are shown at ~10° and 35°N to indicate the active region prior to the discovery of NDS‐2018.

Reference Cheela, from here:


texts:
Would it be possible to get a terribly shaped mirror, like a large sheet of something reflective, give it a general shape like a telescope mirror, but not anywhere near as precisely shaped as in a proper mirror, then use software to correct the image collected by the CCD into likely images?

The software could "learn" by being pointed at various objects , sun, moon, planets, stars, houses, etc, to learn it's own mirror errors, which you could correct, with the correction data saved as a filter,,much like facial and object recognition software operates, then use X number of high end graphics cards to correct the image in real time.
 Seems as though the software correcting for the terribly made mirror would eventually create a filter that would give a good image. Even if the errors required a lot of storage space on drives to create the filter, it should be able to correct the images over time into something recognizable and maybe accurate.

Another thing would be editing software for the image , you could manually or automatically bend the observed objects lines, correction software would straighten or curve lines in initial images, and the correction you apply would be applied to your terrible mirror's error correction filter.   Your terrible mirror could be an old silvered Pyrex plate, or a large piece of Mylar balloon material mounted on a shaped frame, or an intentionally formed piece of sheet metal, or such common things with an inaccurate mirror shape that's not ground to a wavelength of light as current mirrors are. Information not received and reflected by the lousy mirror could be filled in by the   software after it learns for a while.  The cheaper but much larger mirror might fill in some of that lost information~~~


texts: How can I calculate the apparent position of stars as seen from a location on Earth at a specific time?

texts:
I'd like to be able to generate star maps using Python, similar to what is done at YourSky. I believe this is possible with Astropy and the details provided in this question. I can import stars from Hipparcos and use this tutorial to map stars using a Mollweide projection.
What calculations are needed to adjust for location on earth and time of year? Is the Mollweide projection the appropriate projection to use, or would something else be better?

Also related: Correct units to use while plotting mollweide projection of sky chart with RA and Dec values, matplotlib


texts: Could iron rain upset tidally locked WASP76b?

texts:
The Jupiter mass planet WASP76b orbits its 1.5*Sunmass star at 0.03AU and is tidally locked. The day side heats to 2400C which vaporizes metals, including iron observed in its atmosphere. The balmy night side is only 1500C causing ferocious winds which carry the iron vapor from hot to cool side. There it condenses, falling as rain.

Could this redistribution of mass change how the planet faces its star, and what could make that happen? For example, if the winds blew only one direction (I don't know why this would occur) might that act as a small spin that tidal locking forces might try to neutralize?

This is a refugee question from Space Exploration.


texts: Is there a simple, analytical formula for the lunar phase brightness curve?

texts:
Brightness of the lunar disk varies as a function of phase angle. This phenomenon is very well established, as is the increase in brightness at low phase angles.

Is there a simple analytical formula that describes this function? It looks like brightness could be modeled as an exponential as a function of phase angle, modulo the opposition surge.

Thanks.

EDIT: I realize that these effects depend on the wavelength of the reflected light. I'm looking for an average curve, though.


texts:
According to this Wikipedia page, the top five highest mountains on Mars (and the highest on Venus) are all taller than Mount Everest (and Mauna Kea as measured from the ocean floor).

Does a planet's mass or gravity affect the height of it's mountains?  Is there an upper limit that a mountain can reach given the mass or gravity of a planet?


texts:
Are there any plans for the 'Hubble2'? Maybe with an even bigger mirror capable of even finer resolution, to look even deeper into the origins of the universe?

If so, when can we expect to see it in action?


texts: If Jupiter is a gas-giant then why don't its features change?

texts:
A naive question. When we look at Jupiter, we see that its features didn't change largely over many years, for instance, the red-spot. If it is composed of gases and liquids, then why aren't the effects of mixing of these fluids visible?

My intuition is that due to very low temperatures ($-145\, ^{\circ}$C), diffusion of fluids doesn't occur and therefore the superficial appearence of Jupiter remains the same.


texts: Do tides occur on planets like Neptune, having water?

texts:
I mean, we experience tides here on earth because of combined effect of gravitational field of moon and sun. So I thought that tides could also occur on other planets.

Let us consider Neptune where the gas transits into a slushy ice and water layer. The water-ammonia ocean serves as the planet's mantle, and contains more than ten times the mass of Earth. Also it has 14  moons. What I was thinking was that more moons would mean more tidal effect would be seen even if distance from sun has increased.

But then I thought that the moons of Neptune would all have different orbits and different time periods of rotation. So this will definitely impact the extent of tides.

-To what extent will this affect tides?

And how will tides formed on Neptune be different than that  formed on earth? I mean, how will they vary in properties?


texts: Open cluster membership determination via parallaxes

texts:
I'm working in my final course project and I'm using the recently released GAIA DR2 data. I want to determine open clusters membership and I know this has mainly been done  using proper motions and positions, and maybe photometric data.
Since now we have access to parallaxes I was wondering if one could also estimate the cluster membership from them, considering all cluster members must have approximately the same parallax value (if they are to be at the same distance from us). I guess the technique can't be much different to the usual one done with proper motions, but I can't work it out in a rigorous way. Any help is appreciated! Thanks in advance.


texts: Why are Cassegrain telescopes shorter than Newtonian reflecting telescopes?

texts:
Many websites say this is because the effective focal length of the objective is increased by making the secondary mirror convex. This allows a Cassegrain telescope to be shorter than a similarly powered Newtonian.

What I don't understand is that if the focal length is made longer, how come the telescope doesn't have to be made longer too? Could someone explain how the focal length is increased and how this leads to shorter telescopes?


texts: How can they tell no asteriods will hit earth in the next hundreds years?

texts:
I have been thinking about this question :

  How can they tell no asteroids (big enough to create damage) will hit earth in the next few hundred years?

Because, so far, we were unable to get a clear and nice view of a planet of the solar system planet which is not that big, but still bigger than an asteroid. So how can they tell that nothing from the immensity of the Galaxy and Universe, bigger than a few yards, will cross our path and hit us within the next 100 years?

We all remember Chelyabinsk meteor in 2013, or whatever how they called that thing. They never saw that coming but it still caused damage and it was only few meters (± 20 meters according to that page Wiki link), Arround 1,500 injuries and ± 7200 damaged buildings... It's hard to believe that they know how to see something not so much wider than 20 metres wide outside of our solar system.


texts: Question about Hubble parameter (Hubble constant) and measuring it

texts:
I see this question in "An introduction to modern cosmology - Andrew Liddle - Wiley Publication":

In the real Universe the expansion is not completely uniform. Rather,
galaxies exhibit some random motion relative to the overall Hubble
expansion, known as their pecuLiar veLocity and caused by the
gravitational pull of their near neighbours. Supposing that a typical
(eg root mean square) galaxy peculiar velocity is 600 km/s, how far
away would a galaxy have to be before it could be used to determine
the Hubble constant to ten per cent accuracy, supposing
(a) The true
value of the Hubble constant is 100 km/s Mpc?
(b) The true value
of the Hubble constant is 50 km/sMpc ?
Assume in your
calculation that the galaxy distance and red-shift could be measured
exactly. Unfortunately, that is not true of real observations.

I really don't know how to start solving this. What do we need to find Hubble constant. I know $v=H.r$ but I don't know how to calculate the effect of peculiar velocity. we don't know $v$ and $r$ in Hubble formula, how to find $H$?


texts: Has the Earth's wobble around the Earth-Moon barycenter ever been observed by a spacecraft?

texts:
Pluto's motion around the Pluto-Charon barycenter has been imaged by the New Horizons spacecraft:

Has anything like this been imaged of Earth? Yes, the barycenter lies inside of Earth, but it is 3/4th of the distance from the center — more than enough for a noticeable wobble over the course of one orbit.


texts:
I am a beginner in astronomy. In fact, I just bought my first refractor telescope with 60 mm aperture and 600 focal lengths with 4mm, 12.5mm and 20 mm eyepiece and 3x barlow.

Could I get info on android app or book where I can see real-time position of planets and other amazing celestial bodies, I am in the northern hemisphere.


texts:
According to this,

https://en.wikipedia.org/wiki/Intergalactic_star

Rogue stars are theorized to be the intergalactic space because of this,

  The way these stars arise is still a mystery, but the most common
  theory is that the collision of two or more galaxies can toss some
  stars out into the vast empty regions of intergalactic space.

Could a planet be toss from a galaxy just like it's theorized rogue stars are?


texts: How actively is Deep Learning being used in exoplanet identification?

texts:
Papers, like this one from Google, show that Deep Learning and Machine Learning are effective in detecting exoplanets from luminosity data provided by telescopes like TESS or Kepler.

These models seem extremely quick and lightweight. Has it become somewhat of a standard practice to use these on freshly obtained TESS data? If not, why, and what is done with the data instead? Are there drawbacks to using these seemingly accurate models?


texts: Auroras: is there any bump in frequency at certain times of night, or times of year?

texts:
I'm trying to find out if there is a range of times at night, and/or days during the year, in which the probability of seeing an aurora is higher than average.

The aurora section of the British Astronomical Association asserts that there's
a correlation with season (higher probability near equinoxes), and a correlation with 'magnetic midnight'.
http://www.britastro.org/aurora/

Are these assertions correct? If so, what is the definition of magnetic midnight, exactly?


texts: What celestial body (inside the solar system) has the highest flattening ratio?

texts:
As a planet, Saturn has the highest flattening(ellipticity) which is 0.09796. So, it makes Saturn with the largest equatorial bulge as a planet and as such Saturn is the flattest planet.
However, I have encountered this statement from here:

Earth's Moon is even less elliptical, with a flattening of less than
1/825, while Jupiter is visibly oblate at about 1/15 and one of
Saturn's triaxial moons, Telesto, is highly flattened, with f between
1/3 to 1/2 (meaning that the polar diameter is between 50% and 67% of
the equatorial).

So, Telesto has a flattening value even higher than Saturn itself. I couldn't find any other body that has higher flattening value than Telesto. Does that mean Telesto has the highest recorded 'f' value?
Question: What celestial body inside the solar system has the highest recorded flattening value? Is it Telesto?
Note: Most of the asteroids, meteors, comets and small moons have irregular shapes and as such measuring the 'f' value is impossible and may have no useful value. I want to know which body has the highest recorded 'f' value.


texts: When I measure RV in a program for more spectral lines, will it be equivalent? I mean I measure RVs of a line in blue spectral region, RVs of a line in red spectral region... Many thanks.


texts: Is our Solar System moving independently through our galaxy?

texts: I would like know if our Solar System is moving independently through our galaxy or is stuck on the Orion Arm which is revolving around our galaxy? Is our solar system an onboard passenger of the Orion Arm?


texts: Is the turn-off point of the main sequence the same as the terminal-age main sequence?

texts:
The turn-off (TO) point is one tipping point on the Hertzsprung-Russell diagram (HRD) where low-mass stars start to evolve from the main sequence (MS) toward lower temperatures. If I understand it correctly, this is the beginning of the sub-giant phase when the stars no longer have hydrogen burning at the core.

The definition above suggests that the TO point is the same as the terminal age main sequence (TAMS), however, I have not found a source that explicitly states so.

Is the TO point the same as the TAMS?


texts: Can we determine where the north and south magnetic poles are on stars and black holes?

texts: The question is related to this about Are there collected data about the direction of rotation of black holes and the direction of the magnetic field?. Perhaps it is observable for pulsars?


texts: Is the resulting light from a supernova a product of photons bouncing around in the Sun?

texts: I was thinking about how photons formed in the centre of the Sun take quite a long time to exit the surface. And it occurred to me that at the end of a star's life (during a supernova, given that it's big enough) all the photons that had built up in the radiation zone would be emitted at that point. Is the resulting emission of all those built-up photons what produces the great source of light seen during a supernova, or is it simply a contributor?


texts: How do I calculate the elevation angle to the horizon?

texts:
I'm creating an app to visualize the southern area of the moon from a first-person perspective. I'm trying to determine if a point on the surface is a "checkpoint," where the elevation angle to Earth is greater than the elevation angle to the horizon at the same azimuth angle (basically if the Earth if visible). However, I don't know how to calculate the elevation angle to the horizon. I initially thought of using the slope at the current point, but this doesn't work because there could be a point up ahead with a much larger slope, which would block the visibility of the Earth.
All help is appreciated!


texts: A question about star names... E.G. CW Tauri, DZ Bootis, IQ Lupi, EU Eridani

texts:
Take the following examples of star names/identifications:-

Regulus is the common name for a star.

HIP49669 is the Hipparcos ID for the star

HD87901 is the Henry Daper ID for the star

32 Leonis is the Flamsteed ID for the star

Alpha Leonis is the Bayer ID for the star

And now for a probably unrelated stars at random.

Why and how does stars like 'CW Tauri', 'DZ Bootis', 'IQ Lupi', 'EU Eridani' get their name, is there a catalogue for them?  Who assigns their name? Do they individually mean something or randomly chosen letters?  I'm not just after those stars but all stars with similar style naming.

Thanks in advance


texts: Why do objects appear blue while on a neutron star?

texts:
I was playing around in Space Engine recently, and I realized I hadn't yet landed on a neutron star. This seemed like a very sensible thing to do, so I did it and chose a (relatively) well-known one called Black Widow on which to conduct my adventure. As I landed, I saw mostly expected things-it bent space-time, was rotating very fast, etc. One thing I didn't expect, however, was that everything was blue. Everything. I don't mean the star itself appeared blue, I mean as I looked off the star into the galaxy all the stars appeared blue. I searched for a while but didn't find anything on the Internet. Anyways, does anyone here know why this is happening?
Edit: I have a theory —probably wrong— but maybe because of the warping of spacetime near the neutron star, photons are getting compressed and blueshifted.


texts: Is it only possible to look at solar systems with stars at least as old as ours to be able to find intelligent life?

texts: Assuming the speed it takes to development intelligent life is the same in all solar systems, would we need to look at exoplanets with stars as old or older than ours to find intelligent life? A young star would be assumed to have been surrounded by planets that are relatively new and haven’t had time to develop intelligent life. Visiting those planets with young stars relative to the sun would most likely only give us planets with prehistoric life.


texts: What would the night sky look like if the interstellar medium didn't exist to absorb or block light?

texts: I was curious about how much brighter it would be and how much further we could see.


texts: Using a refractor telescope at 200x, how close will an object appear at four miles away? Is there a table out there enabling you to calculate apparent seeing by filling in known variables?


texts: There were so many Apollo Missions, and they landed on the moon (so they say). When astronauts came back to Earth from the moon, they brought Moon rock samples. Where are these moon rocks/samples now, and where can we see them?


texts: Is the gravitational field of the sun uniform?

texts: I understand that rocky bodies in the solar system all exhibit gravitational anomalies. Does the sun exhibit any gravitational anomalies?  If so are they distinct enough that it effects the orbit of the Parker Solar Probe?


texts: Could Hot Jupiter systems sustain Trojans?

texts:
My understanding is that there is a gravitationally stable region between the Sun and Mercury where asteroids could - in theory - orbit for long periods without being perturbed. However these hypothetical vulcanoids are seemingly non-existent; it being likely that their orbits decay through other means besides the influence of a planet, such as the Yarkovsky effect. We also have trojan asteroids, which share the orbits of planets such as Jupiter but spend their time in the leading and trailing Lagrange Points, keeping their orbits stable.

If a Hot Jupiter such as 51 Pegasi b were to host trojan asteroids, would their proximity to the planet allow their orbits to remain stable for longer, or would their orbits decay regardless? If a Hot Jupiter migrated inwards towards its star, is it more likely to have swept away any possible trojans?


texts:
I have been reading about celestial mechanics and particularly about planetary orbits. I understand that a planet's orbit can be tilted (pitched) with respect to the Earth's ecliptic and that it might precess (yaw) over time. But I have not come across any indication that another planet's orbital plane might be rolled with respect to the Earth's.

I have also found references to Keplerian orbital elements, but I don't see that any of them indicate roll. Am I misunderstanding the situation? If not, would someone point me at an elementary resource where I can learn about this?


texts: Difference in observing hot stars that have been reddened and stars that are cool and red

texts:
How do astronomers distinguish hot stars, reddened by the interstellar light absorption, from the actual cold
red stars?


texts: How can space expand in accelerating speed when dark energy is constant?

texts:
I came to know that dark energy is constant.As mentioned in the Friedmann equations

How can a constant energy cause an accelerating rate of expansion in the universe?


texts: How to calculate the approximate angular (how many degrees across?) from an image in DS9 rendering?


texts: Can the "haze" of a mirror telescope be quantified?

texts:
When reading Why was StDr56 discovered only now? and its answers and comments, I realized that refractor telescopes, and in particular the Dragonfly Telephoto Array are a great tool to find nebula and other faint objects. The proud parents at the Dunlap Institute summarize their technique nicely:

Dragonfly images a galaxy through multiple lenses simultaneously—akin to a dragonfly’s compound eye—enabling further removal of unwanted light. The result is an image in which extremely faint galaxy structure is visible.

Why are Earth-bound mirror telescopes not able to see such objects? To use uhoh's words:

[T]he back story there is that refractors were better suited than reflectors because nano-roughness of silvered mirrors produces a faint haze of scattered starlight that competes with natural skyglow to "fog" exposures and hide objects with low surface brightness.

This finally brings me to my question: How can this haze originating from the mirror telescope itself (and not from atmospheric effects) be quantified? Why does the nano-roughness of a mirror disturbes the image more than optical abberation of the lenses in a refractor telescope? Is it really only the nano-roughness? Or is it maybe also the support of the secondary mirror which is responsible for the "spikes" in pictures of stars?
References

Deciding optical factors between a refractive and reflective space telescope optics as a function of aperture? (visible light)
What are the benefits of a large refracting telescope?
Deciding optical factors between a refractive and reflective space telescope optics as a function of aperture? (visible light)
Shany Danieli et al. The Dragonfly Wide Field Survey. I. Telescope, Survey Design and Data Characterization
Deborah M. Lokhorst et al. Wide-field ultra-narrow-bandpass imaging with the Dragonfly Telephoto Array
Roberto Abraham et al. Future Prospects: Deep Imaging of Galaxy Outskirts using Telescopes Large and Small


texts: Which stellar properties can we describe as "first principles" in which we can derive the rest?

texts:
Mass, size, temperature, luminosity, chemical composition, the initial abundance of the molecular cloud, distance, brightness, age, and evolutionary cycle can all be used to characterize a star. A star's brightness is dependent upon its distance and luminosity, so brightness is not a "first principle"; however, there are some properties that seem less obvious in determining their dependencies. For example, chemical composition and temperature seem to be at a constant interplay. Does one always inform the other? Chemical composition and mass influence a star's evolutionary cycle, so it's evolution through the HR diagram is also not a first principle (from my understanding).
For fun, if we wanted to describe a star in the most simplistic way possible, which properties would we need to know? My assumption would be the initial chemical composition when the star was made and its initial mass. If we wanted to know the star's brightness for observational purposes we would also need to know the distance, but this isn't a fundamental property of the star. In other words, what are the basic properties we need to know to extrapolate the rest? I'm, betting on mass and initial chemical composition, but am unsure about temperature. We can throw in distance for observing properties but I was mainly using this as an example.


texts:
chemistry tells us that when mixing hydrogen and oxygen the result is an explosion and water.

my question is: does this happen on astronomical scale? for example, did they ever observe planet-size hydrogen cloud collide with planet-size oxygen cloud to produce a huge explosion and planet made primary of water?


texts: Theoretically, can a solar system evolve around lagrange points

texts:
My question is, during the evolution of a solar system is it possible to end up with a massive planet around a star with two small planets around their $L_4$ and $L_5$.
Since we know it is not possible to have any bodies around $L_1, L_2, L_3$ due to their low stability, hence any planet trying to evolve their can be easily nudges out of its position.


texts: Are there standard algorithms and procedures for creating unique sky maps based on latitude/longitude/date/time?

texts:
I am trying to build an astronomy app that will use the user's latitude and longitude, along with the current date and time, to create a 3D view of the celestial sphere as seen based on that data.  However, the information I've found so far has been very general and less-than-practical, and has included virtually nothing about how to take date and time into account.

Does anybody know of a more concrete source of information on sky mapping in this way?


texts: How do I build a stargazing aficionado's Sun funnel to observe our nearest star safely?

texts:
How do I observe the Sun safely, with tools I could build myself and without breaking the bank? If I wanted to build a Sun funnel on my own and use it on my enthusiast grade telescope, how would I do that?

What supplies and tools would I need, how do I attach it to my telescope so it can be applied to it at will, and are there any other, simpler yet safe ways to observe the Sun and its activity with my telescope? This is approximately what I had in mind:

How do I build something like that? I'm primarily interested in observing sunspots, but would also like to know, if there is any way for me to safely observe Sun's coronal activity to any appreciable detail with an enthusiast grade newtonian/dobsonian telescope?

Additionally, could I project the telescope's image directly on some screen behind it, without having to use any intermediary digital equipment, like a recording camera and a digital light projector?


texts: Relation between oscillator strengths $\log{gf}$ and the Einstein $A$-coefficient, rotational quantum number,

texts: I'm analyzing the spectra of M dwarfs. Some authors characterize the lines with the oscillator strengths $\log{gf}$ while others follow different paths with the Einstein $A$-coefficient. I would like to know if there is  relation between the oscillator strengths $\log{gf}$, and the Einstein $A$-coefficient, rotational quantum number J', vibrational levels with the Hönl-London, factors or similar parameters.


texts: Are there non thermal filaments outside our Galaxy?

texts: The question says it all: are there observations of something like non thermal filaments in other Galaxies other than our?


texts: Does the Zwicky Transient Facility only run when triggered by a cell phone?

texts:
A really enjoyable interview with Mansi Kasliwal & Samaya Nissanke ("From discovery to making precision measurements") is available as a short audio podcast in the BBC News article Gravitational waves hunt now in overdrive describes the very recent gravitational wave events and the way optical searches for the source were initiated by pressing a "go button" on a cell phone!

It's a excerpt from the BBC's Science in Action episode What is behind the Indian Ocean Cyclones?

The article is quite a good read as well, and talks about the Zwicky Transient Facility (ZTF), based on the 48-inch Samuel Oschin Schmidt telescope with several upgrades including a state of the art silicon CCD array replacing the 14 inch square photographic plates it originally used, faster slewing and AI-based recognition of candidate objects.

The huge aperture allows for almost 50 square degree field to be checked down to +20 magnitude every five minutes. That's about one steradian in 5 hours. According to the podcast, it can run as fast as 4000 square degrees per hour, about 1.2 sr/h presumably with a brighter limiting magnitude.

Question: Does the ZTF only start surveying when triggered by a cellphone or other alert, or does it continue to search for new objects and events on some nominal routine whenever there is good visibility?


texts: How probably is it that galaxies will extinguish?

texts: In the nebulaes of galaxies are stars born, but the gasses and dust they are made of comes from exploded stars (fe supernovas). So it looks like these processes can go on continuesly. But is that really the case, or does according to entropy(?) galaxies extinguish because fe the galaxie went too big so gravity has no opportunity to form other stars any more. And before colliding with other galaxies it is passed away. So is there any sign that galaxies are getting smaller or less active?


texts:
After a supernova neutrinos get released by electron capture,and they escape in a flood.

My guess is because they have tiny masses and get momentum from momentum conservation.

  However, the huge number of neutrinos it emits carry away so much energy that the temperature of an isolated neutron star falls within a few years to around $10^6$ kelvin.

Reference : Wikipedia,Original(wikipedia reference)
Wouldn't most of the neutrinos scatter after supernova almost instantaneously before a formation of a neutron star?


texts: What were the 2 satellites I saw this morning?

texts:
This morning at 6:03am Israel time (3:03 UTC) I saw, simultaneously, what appeared to be 2 satellites streaking across the sky directly overhead. If I remember correctly, they were both coming from NW (but it was early).

Does anybody know what they were, or how I can find out?

I live in Mitzpe Netofa, lon/lat about 35.39/32.80.


texts: Why hasn't the "9th Planet" been detected already?

texts: In the comments to this question, there was considerable doubt placed as to the subject of if the so called "9th planet" really exists. That wasn't really the intent of the previous question, so I ask this. Why hasn't this "9th planet" been detected before now, if it even exists?


texts: Is it possible to observe strong gravitational lensing with amateur telescopes?

texts:
Strong gravitational lens systems like the Cosmic Horseshoe have been imaged by scientific space telescopes, but have any amateur astronomers accomplished this?
Or are amateur/small ground based telescopes not suited for this?


texts: How to get SOHO Satellite images' coordinates?

texts:
I'm working with images from LASCO C3 coronagraph

I'm able to download pictures from LASCO C3 using this form
https://sohodata.nascom.nasa.gov/cgi-bin/data_query

Then, I want to do some analysis of CMEs on this pictures and determine some of their parameters, such as direction and speed (i know that is better to use STEREO A\B for that purposes), but also I need exact coordinates of SOHO station to determine the direction of the ejection in space

How can I get the coordinates of the station for these pictures?


texts: Position of the Sun in the constellation Pisces around the year 1500

texts: I am reading a book on ancient astronomy and it claims that around the year 1500 the position of the sun, at the time of the spring equinox, was on the tail end of the second fish in the constellation of Pisces. Now I understand this might be more guess work than anything else but I am wondering if this claim could be even remotely true. I don't even know where to begin in calculating this. Any help is appreciated.


texts:
How can I derive limit magnitude in 5sigma/2arcsec ?
I have the limit magnitude in 5sigma which derive from the magnitude with SNR reach 5.
But I can not understand what the meaning of dividing 2arcsec.


texts:
My question is very similar to this one although the answer is not what I was looking for.
Basically I'm working in a space game (KSP) and I'm making it multiplayer. The clients send a packet with their orbital parameters at a interval (30 miliseconds by default) but between those packets I want to interpolate and draw an orbit between those 2 packets.

For normal vectors or speed I use linear interpolation:

private static float Lerp(float v0, float v1, float t)
{
    return (1 - t) * v0 + t * v1;
}

But It doesn't work well when I work with orbits

var inclination = Lerp(inclination, Target.inclination, lerpPercentage),
var eccentricity = Lerp(eccentricity, Target.eccentricity, lerpPercentage),
var semiMajorAxis = Lerp(semiMajorAxis, Target.semiMajorAxis, lerpPercentage),
var LAN = Lerp(LAN, Target.LAN, lerpPercentage),
var argumentOfPeriapsis = Lerp(argumentOfPeriapsis, Target.argumentOfPeriapsis, lerpPercentage),
var meanAnomalyAtEpoch = Lerp(meanAnomalyAtEpoch, Target.meanAnomalyAtEpoch, lerpPercentage),
var epoch = Lerp(epoch, Target.epoch, lerpPercentage),

What function can I use to interpolate them?


texts: Can lightning occur in stars like the Sun?

texts:
In the Wikipedia article about lightining, the following explanation is given about the electrification process in clouds:

The details of the charging process are still being studied by
scientists, but there is general agreement on some of the basic
concepts of thunderstorm electrification. The main charging area in a
thunderstorm occurs in the central part of the storm where air is
moving upward rapidly (updraft) and temperatures range from −15 to −25
°C (5 to −13 °F); see Figure 1. In that area, the combination of
temperature and rapid upward air movement produces a mixture of
super-cooled cloud droplets (small water droplets below freezing),
small ice crystals, and graupel (soft hail). The updraft carries the
super-cooled cloud droplets and very small ice crystals upward. At the
same time, the graupel, which is considerably larger and denser, tends
to fall or be suspended in the rising air.
The differences in the movement of the precipitation cause collisions
to occur. When the rising ice crystals collide with graupel, the ice
crystals become positively charged and the graupel becomes negatively
charged; see Figure 2. The updraft carries the positively charged ice
crystals upward toward the top of the storm cloud. The larger and
denser graupel is either suspended in the middle of the thunderstorm
cloud or falls toward the lower part of the storm.

This mechanism seems to rule out the possibility of lightning in absence of a condensed phase (liquid droplets/solid crystals). That makes me wonder, is lightning truly impossible in stars hot enough to be fully gaseous, like our Sun? Or could a alternative mechanism generate lightning in such environment.
Even in absence of any alternative mechanisms, I think lightning still could form at least in small, cold stars, or in old brown dwarfs. What would be the size/age threshold?


texts: Is there anywhere I can find some kind of database on all known stars and their properties (mass, surface temperature, radius, and luminosity)?

texts:
I have been looking for some kind of collection of all known stars and their individual respective mass/radius/temperature/and luminosity, can you link me to one if it exists?

My goal is to write an algorithm that creates polynomial functions that calculate a stars temp/lum/radius based on mass. I know there are existing equations, however the ones I have found are more troublesome and imprecise compared to if I could use polynomial functions I create myself.

The Hertzsprung-Russel diagram ( http://upload.wikimedia.org/wikipedia/commons/1/17/Hertzsprung-Russel_StarData.png ) is a great example of representation of what data I need, however it's axes are not constant, so I can not visually gather accurate sample data to deduce any functions.

Edit: Essentially even a large quantity of estimates will suffice. I intend to use this data to generate a semi-realistic galaxy for an MMO I am developing, so it doesn't by any means need to be perfect.


texts: Does the Reflection Method for Looking at the Sun Work For Refractors?

texts: I own a newtonian reflector and occasionally use it (using the reflection method with paper) for looking at the sun. I happen to also own a refractor, but I'm not exactly sure if the reflection method will damage the equipment (notably the lens on the refractor) if I do.


texts: I know Andromeda is our nearest galaxy. But how many known galaxies have been discovered and what are they?


texts: How long would it take for a rogue planet to evaporate in the late stages of the Universe?

texts:
I've read once a popular science book, in which the author calculated how long would it take for the most massive black holes to evaporate because of Hawking radiation. He claimed that after that time the Universe will be the soup filled only with elementary particles.

However, what would happen with celestial bodies that aren't black holes? For example, a rogue planet of the size of Earth, drifting somewhere in deep space, in an extremely cold Universe? What known effects would cause that planet to evaporate? How long would it take?


texts: Why do heavy mid-sized stars become more luminous as they leave the subgiant branch entering the red-giant branch?

texts:
Wikipedia says:
For stars heavier than the around a solar mass the "outer layers cool sufficiently to become opaque" which "cause the hydrogen shell to increase in temperature and the luminosity of the star to increase, at which point the star expands onto the red-giant branch."
To my understanding, the source of luminosity is the H shell burning. If the outer layers become opaque (ie not transparent), why does the star become more luminous in this process?


texts: Why objects are uniquely defined by their right ascention and declination?

texts:
I've just started studiyng Astronomy.

I understood how I would measure Right Ascention and Declination: for the first one I'd trace an Hour cirlce to the Celestial Equator, and then, compute the angle from this point and the Vernal Equinox; while the second one is the angle subtended by the object and the intersection of the Hour Circle with the Celestial Equator.

So, during the night, stars will change their Right Ascension value? Does this means this coordinate system is not fixed with respect to the stars?

If so, why people store the RA/Dec to find objects?
For instance, I know  the RA/Dec of the NGC 5585 Galaxy ( http://en.wikipedia.org/wiki/NGC_5585 ), but how can I use this information, if the RA changes during the night?


texts: What qualifies as a good place for stargazing, i.e. with least light pollution?

texts:
I know that minimal light pollution is a must for stargazing, and a place which is away from civilization is better.

Does altitude of a place matter for light pollution?

Does it affect the quality of star gazing?


texts: Element Abundance Related To Star Explosions

texts:
Sorry if this question is too basic, but as I learned about how supernovae are means of producing heavy elements I began to wonder "What would happen if stars didn't explode, i.e. undergo supernova"? Hydrogen and Helium would definitely dominate element abundance at a higher level, but how much carbon and other heavier elements be produced? Are there intermediate stars of enough mass that we could reach all the way to Iron?

Now what would happen if stars never reached the planetary nebulae phase? Would the only elements present be Hydrogen and Helium?


texts: Why can't we just build a lunar base instead of going through the hassle of going to Mars?

texts: Why don't we just build a base on the moon then Mars.It's much closer and the trip there only takes a day or two instead of 7 months one-way to Mars ( and that's if everything goes perfect).Elon Musk could just go to the moon and then head to Mars right? Even though the lunar surface gets bombarded with radiation it still seems easier than going to Mars(which also has a lot of radiation problems too) and what if there's a shortage of food or water,or something goes wrong on the planet and you have to wait 7 months for help? Or am I being overreactive?


texts: VSOP for exosatellites? (Io, Titan, Ariel, etc)

texts:
VSOP87 (and the subsequent VSOP2000 and VSOP2013) provide reasonably
accurate planetary positions while still maintaining a small file size
compared to the Chebyshev polynomial files.

VSOP includes our moon, but has anyone created something similar for
other planets' moons (such as Jupiter's Io, Saturn's Titan, and
Uranus' Ariel)?

I'm thinking about trying to create something like this and wanted to
check that it hadn't already been done.


texts: Are the dark grey areas on the moon formed from the last lava flows from volcanoes? And that is why there are hardly any craters in those dark grey areas because the lava has covered the old craters?And If so are there still active volcanoes that are still flowing to this day?


texts: Does the redshifting of photons from the Universe's expansion violate conservation of momentum?

texts:
The energy-momentum relation,

$$E^2 = m^2c^4 +p^2c^2,$$

lets us derive the momentum of a massless particle:

$$p = \frac{E}{c} = \frac{h\nu}{c}$$

However, the expansion of the Universe redshifts light. This should decrease the momentum of photons. Where would the momentum go, in order for conservation of momentum to hold?


texts: Is there a name for a planet and its moons/satellites?

texts: I'm wondering if there's a name that encapsulates the concept of a planet and the objects that orbit in its gravity. There's a solar system that encapsulates a star and its multiple planets and other objects, but I don't think that "solar system" describes the Earth and its moon, or Jupiter and it's many moons, for example.


texts:
I found this page: http://phys.org/space-news/ . It seems to me pretty good page with interesting news and so on and I like that it is free. But I noticed in comments people arguing about the validity of the information and so on. Are they just "trolls" or is this page really bad source of information, if that is so, how much can I trust it?
Thanks in advance!


texts:
I am currently designing star and planet systems in the RPG framework GURPS. This game system has a very elaborate set of rules to set up a star system, complete with planets and the like. However, one (for me at least) critical issue is not addressed in the book: The argument of perihelion.

Now, since I am writing a program to generate these systems for me, I would like to know what steps I can take to make a planet system as realistic as possible. Looking at data from our own planet system, the argument of perihelion looks to be pretty evenly distributed over all angles $[0, 2\pi)$.

Is there scientific evidence that this is actually the case, or are there any good suggestions on how I could proceed with my program?

(The related question on RPG.SE can be found here.)


texts: Can a planet with a hydrogen atmosphere have a water ocean with dissolved oxygen?

texts: Reading up on rogue planets (i. e. planets not orbiting a star), it turns out that a rogue Super-Earth with a sufficiently dense hydrogen atmosphere could retain its internal heat and have oceans/lakes of liquid water. What I'd like to know is whether those oceans could contain dissolved oxygen in equilibrium. Please advise if this should be best posted to Chemistry...


texts: How co-planar and co-rotatory are the Milky Way and its constituents?

texts:
All the planets in the solar system rotate roughly in a plane that intersects the sun.
Stars in the Milky Way rotate around its centre forming a rough planar disk.
Question
Are these planes all parallel? I.e. Do planets of all stars rotate in planes parallel to the plane of the galaxy? Do they rotate in the same direction?
If so, is it
(a) because the whole galaxy evolved from a spinning mass so it naturally turned out that way
(b) because, over time, the 'wheels' that were spinning on other axes were somehow dragged into alignment
(c) Nobody knows
(d) Something else


texts: In the milky way which star(s) are farthest from galactic plane?

texts:
I am looking for at least one star on each of the side of the galactic plane. I understand there would be an error tolerance. So, please do not hesitate if the answer is not exact.  Preferably, please refer to a paper. I searched on the internet and only found the farthest stars from the earth.
By "in the milky way" I mean any star that rotates around the center of the milky way. Among (stars of) satellite galaxies of milky-way, the confirmed galaxies that are rotating around milky-way exclusively are included.


texts: I tried searching on the internet and could not find anything, so does anyone know if there's a website which tracks and shows Betelgeuse's magnitude daily?  I just went out today and saw that it's now about the same brightness as Bellatrix.


texts: What is the bright star or planet in eastern sky on dec 18 2018?

texts: What is the bright star or planet in eastern sky on Dec 18 2018 in Laurens SC. It is very bright and beautiful on a clear night. I have been seeing it for about a month or more. It seems to follow the same path as the moon. This object is sighted at sundown to sunset. Is it a star or a planet? It is very bright and does not twinkle.


texts: Can an observer on Earth only see half of the sky?

texts:
Is this the following statement true?

  An observer on earth only may see half of sky from the northern or southern hemisphere, and even if the observer stands on the equator on top of a very high mountain, he will hardly be able to see all the stars in the sky in given period!

Do most globe-like objects in space have this property?

I'd appreciate any more remarks on the subject.


texts: What's the distance between Venus and Jupiter?

texts:
What is the minimum, maximum and average distance of the Venus and Jupiter?

I only found 670,130,000 km and 670,198,000 km as an average distance (here and here).


texts: How to differentiate elements that have same spectral lines in a star?

texts: Suppose that iron and calcium have a spectral line with the same wavelength. How would you determine which element is present in the atmosphere of a star if you found this line in its spectrum?


texts:
What I understood about it till now is that space-time fabric is kind of broken there. Please tell me whether I am correct.

If it's true then does it mean that perception of time will stop there?
I really can't get what broken space fabric is like. If it's a hole then how is matter supposed to be present inside that?
Is a black hole a discontinuity?


texts:
I'm thinking of putting a large wall paper with an astronomical motive on a wall. I found quite a number of wall papers by various vendors, but most of them are obviously computer generated images, which is a no-go. It must be an image of an astronomical object, a nebula or a galaxy. (There's also a size requirement, not under 236 x 370 cm, so please do not suggest I use a printed image fitting a common frame format).

Now I found this wall paper. To my eyes it does not obviously look like CGI. But there are no diffraction artifacts visible for the bright stars; perfect circles it seems.

Can anyone identify the object?


texts:
For a project I'm doing, I need to implement the VSOP-2000 ephemeris for the Moon. However, unlike VSOP-87, there is little to no documentation online on how to use the data. For example, here is the first line of the x-term for the Moon in VSOP-2000:

  1   0  0  1  0   0  0  0  0   0  1  0  0   0  0  0  0   0  0  0  0     -.1053243070325313D-09     -.2560241101399878D-02

This is very different from VSOP-87, which I know how to use. Are there any resources online that could inform me on how to use this?


texts: What else could the Event Horizon Telescope Observe?

texts:
The Event Horizon Telescope was made possible in order to observe the details of supermassive black holes. This took a huge amount of work installing extra telescopes and developing the hardware and software needed to do VLBI at such short wavelengths. They have achieved spatial resolution around 25 micro arc seconds, comparable to the astrometric data from the Gaia space probe, but optimised for very different purposes.

So my question is what else could they usefully observe? What scientific targets have interesting detail at that angular scale and emit enough radiation at that wavelength to be observable?


texts: Colossus telescope, trying to outsmart aliens?

texts:
I was listening to Jeff Kuhn's talk
on SETI's Colossus telescope project.

Background:

He explains his theory that a civilization living somewhere the galaxy would want to hide, and thus would shortly learn to avoid broadcasting radio signals all over the galaxy, so as to avoid attracting attention (presumably to avoid inter-stellar predators).

Then he comes up with a great idea; due to the second law of thermodynamics, they would have to dissipate heat-energy, and thus, one can detect them anyway, because they have no way to hide this heat-energy. This, particularly when they are a Type I civilization, and nearing Type II; in this case, to avoid global warming, they would capture and use almost all solar energy, and emit an equivalent amount heat-energy.

Thus he proposes a telescope to focus on single stars, which would be capable of detecting this heat-energy (by the distinctive infrared light emmited).

My question:

If a civilization was smart enough to hide all of its radio signals, wouldn't they know that they cannot avoid emitting heat-energy? Thus their predators would be able to find them anyway, and thus, it is pointless to hide the radio signals?

Therefore, we should already be seeing their radio signals, and this telescope is being built for a theory with some holes.

Note: I am not suggesting that the telescope shouldn't be built; I think it could have other very valuable uses, and it would also be interesting to eliminate the theory if it is indeed incorrect (or prove it correct ... somehow). I am just asking if there might be justifications for the theory, in light of my point-in-question, which I am missing.


texts: Are Barlow Lenses Good For Deep Sky Observing?

texts:
I'm using a 750mm (focal length) by 150mm (aperture) newtonian reflector and I've been curious about using Barlow lenses on deep sky objects.

Some of the astronomers at my local observatory say that if you get the lens selection correct so you don't lose any light through the eyepiece, you don't need a Barlow lens. While others say that the Barlow lens doubling the focal length of the telescope allows me to see deep sky objects better than without it.

So, is a Barlow lens an effective tool for deep sky observing? If not, what should I use it for?

Note: I already have a 2x Barlow lens.


texts: Problem with Tychonian model of geocentric universe?

texts:
Just like other proposed models of universe in history, Since Tycho's aren't being used, there MUST be any flaws in compare with widely agreed today understanding
Is there any detailed reference criticizing his concept? Moreover in recent years? I've been searching for awhile by now but couldn't find one
If universe is both isotropic & homogeneous, shouldn't Tycho model be just fine for now? We simply take current model, but using earth as perspective. The rest still maintain the same

Or no?
edit: I think i missed Tycho's whole idea. I thought all the time he was referring to rotating earth, but after @James answer and some reading it doesn't seems so. My central question is on the assumption that his system have rotating earth. If it does, what likely be the problem?


texts: Stellar systems: what is the difference between virial, dynamical and thermodynamic equilibrium?

texts:
I'm currently going through Binney & Tremaine (2008) on my own to learn about stellar dynamics. I also have been perusing additional online resources such as this scholarpedia wiki.

Often when distinguishing between collision-less vs collisional stellar systems, the virial theorem is invoked along with the equations for "crossing time" (also known as "dynamical time") and "relaxation time." A large galaxy is said to be collision-less because its relaxation time is many orders of magnitude higher than its age, whereas a dense stellar system (e.g., a globular cluster) is collisional because its relaxation time is less than its age.

But what is the relationship between this so-called "relaxed" state and virial, dynamical, and thermodynamic equilibrium? What do the three different kinds of equilibria intuitively mean?

For example, I have heard that large galaxies are assumed to be in virial equilibrium and then people derive "dynamical masses" (why not "virial masses"?). What would it take and/or mean for a large elliptical galaxy to be not just in virial equilibrium, but also in dynamical or thermodynamic equilibrium?


texts: Why does the Moon sometimes look Yellow?

texts:
My friend and I both noticed that the Moon looked yellow Yesterday, but it wasn't like that the same time the day before, as far as I remember.

Does the Moon sometimes look Yellow? If it does, why does it?


texts:
What's the time the sun takes in order to rise? (The time in which the solar disk crosses the horizon)
How does this time depend on local latitude and the sun's declination?
Assume that we're at sea level, and we ignore refraction and other atmospheric processes. (solar disk's altitude approximated with 0)


texts: Is it practical to hand grind a convex parabolic or hyperbolic mirror?

texts:
I know it's practical to hand grind a convex spherical mirror and that it's practical to make a concave parabolic mirror from a spherical one. But as I understand it, the procedure for doing so depend on tracking progress by using interference patters generated by focusing light off the mirror, and that procedure clearly can't be used (unmodified) with a convex mirror.

Short of floating the blank in a bath of index of refraction matched optical fluid and apply the concave procedure to the back side, does anyone know of a way to do that sort of grinding?

Also, I've never actually run across a procedure for finishing a hyperbolic mirror for either convex or concave, though I haven't spent much time searching on that one.


texts: I know that Venus is visible during sunset and sunrise, but is it also visible in deep dark night?


texts: We know that a black hole behaves like a whirlpool or a tornado or any of the other rotating phenomena we experience on Earth.But the thing is, all these phenomena, except the black hole, are 2-Dimensional (plus 1 dimension of time) rotating vortices, they move objects from 2D planes to other 2D planes instantly, but through a 3D medium. My question is this, since a black hole is a rotating sphere(3D for that matter, plus 1D of time), does it mean that its endpoint in the vortex is 5D?


texts: What range of exit pupils work for observing the full moon?

texts:
I'm observing the full moon, from a major city, with heavy light pollution and dust.

The objective size is fixed, for this comparison, something between 4 and 6 inches. The question is about the tradeoff between magnification and dimness of the image. I'd like to know what range of exit pupils works best. Again, the goal is to observe the full moon.

To put it differently:

What's the smallest exit pupil at which the moon gets so dim that you can't take advantage of the increased magnification? ("Empty magnification").
What's the largest exit pupil at which the moon is bright enough, so a larger exit pupil doesn't help?

The only reference I could find is this, which claims that 1-2mm works best for the moon. Is that correct?


texts:
This question is about design aspects of large radio telescope dishes which allow them to flex under the influence of gravity as they change elevation angle, and still maintain good optical performance at short wavelengths - on the order of a centimeter or less.

What is a radio "homology telescope" and is the 500m dish in China one?

Background:

I was reading about radio astronomy for background on this and this question. In this informative and entertaining NRAO page I saw the term homology telescope for the first time, so I immediately select-right-click-serched it. At first I was confused by these Mathematics Stackexchange and Stanford Bio-X links:

homology of mapping telescope of a monoid
action of a monoid on a mapping telescope
Genome Space Telescope: Bringing DNA Sequence Homology into the 21st Century

until I realizes that these quit different usages of homology and/or telescope :)

I found the following explanation in Tools of Radio Astronomy by  Thomas Wilson, Kristen Rohlfs and Susanne Huettemeister (Hüttemeister) particularly concise and helpful:

  7.5 The Practical Design of Parabolic Reflectors

  7.5.1 General Considerations

  Measurements of the mechanical properties of an antenna are of importance for its performance. This is especially true if the antenna deforms homologously. By Homology it is meant that, at various elevations, the main reflector deforms from one paraboloid into another. Today, homology is an intrinsic part of the design of all symmetric reflectors.

Later in the same subsection:

  The design of an offset paraboloid has, however, complications. Since the design has less symmetry homology is more difficult to achieve and therefore active, real time adjustments of the surface are needed if the design limit of 7 mm or perhaps 3mm wavelength is to be reached. This will be accomplished by an actuator system controlled in real time by a laser measuring system. But for longer wavelengths, the GBT will not require active surface adjustment (Fig. 7.10).

Here is a screen capture of Figure 7.10 from google

note: There are a number of nice photos and some discussion of the Green Bank Telescope and discussion of it's homology (homologusness?) on the NRAO page where I started, as well.

So here is the question-cluster that I'm currently stuck on.

1) If off-axis telescopes require active mechanical adjustments to maintain a homologous paraboloid figure, do the on-axis telescopes mentioned do it passively - by mechanical design alone? They naturally droop - by design - differently at different elevations (different angles above the horizon) in order to retain a paraboloid figure?

2) For the passive design, is it a) the same paraboloid but just a different section, b) or another paraboloid with the same focal point, or c) has a different focal point and therefore requires axial movement of the secondary mirror or feeds?

3) is the nearly-completed 500m dish in China (FAST) a homology telescope? I know it has a lot of articulation and works off axis, but the word spherical is in the name and the receiver/feed translates laterally. Is it still using the principle of homology, but in a different way?


texts: What scales and types of EM and gravitational radiation do we expect to be given off by a black hole, in the final stages of evaporation?

texts:
In theory, black holes of all sizes eventually evaporate, due to quantum processes close to the event horizon that result in net emissions that appear to come from the black hole (but actually originate just outside it), and which also reduce its mass.
This suggests that subject to rotation and charge, all black holes that evaporate in isolation, in theory behave identically or at least probably very similarly in their final moments.
But what does theory say about the nature of those emissions in the last seconds/milliseconds/attoseconds of an evaporating black hole's life? For example, power output/intensity, spectrum, periodicity if any (eg if rotating), and division between EM and gravitational?
And what time scale might we focus on, in theory, if we wanted to observe interesting end-of-life phenomena? (By which I mean, for inspiralling BH we observe on the order of the last few tens of seconds with most phenomena appearing more visibly in the last 10 or so ms, what would the "most interesting observational interval" be for end of life BH?)


texts: What is the galaxy M87 doing these days?

texts: The massive elliptical galaxy M87 in the Virgo cluster is 53,490,000 light years away. It also contains one of the largest, heaviest supermassive black holes in the known Universe. But it's also my understanding that the stellar population of this galaxy is mostly old, red supergiants. Is there any evidence for new star formation in M87? If there isn't, what is the fate of this galaxy and what is it like in modern times? That may be impossible to know for sure but what I wonder is if the remaining stars and matter in the galaxy have been swallowed up by central black hole which may be thousands of lightyears across by now.


texts: Do massive OB stars accrete mass the same way as the black holes they turn into do?

texts:
It is often said, in spite of sci fi often having illustrated the opposite, that stellar mass black holes do not gravitationally attract material in their environment into themselves anymore than a star with similar mass does. But how and why do blue stars of about 8-10 or more Solar masses which turn into black holes, change how frequently and observably they accrete material from their environment when they transform into BH? Maybe because the supernova ejects material, some of which doesn't get far and is re-accreted when the stellar wind ceases?

BH's are visible when they have active accretion disks. Do massive O and B stars also have such accretion disks as frequently?


texts: How long before Phobos reaches the Roche limit of Mars?

texts: Phobos orbits really close to Mars, so close that one Phobos period is shorter than one sol. Due to tidal friction, it is also getting closer and closer to Mars. How much time will it take before Phobos reaches the Roche limit of Mars?


texts: How would Alpha Centauri A appear from the surface of Alpha Centauri Bb?

texts:
I'm trying to imagine what a hypothetical observer on the surface of Alpha Centauri Bb would see in the daytime sky. I know it would vary depending on the orbit of b around B, as well as the position of B and A in relation to each other.

What would the "sun" in the sky look like at different times on Bb? I know that at times B and A would overlap and appear as a single sun, but what about when they don't?


texts: Printed Circuit Board manufacturing file for Radio Jove?

texts:
I woild like to build a Radio Jove receiver whose design is available on NASA website. However, I don't want to purchase the receiver, I would like to make it, but but I don't have any knowledge about the PCB design. May
someone please help me to get the PCB manufacturing file?


texts: Why could I so easily see and photograph such a bright totally eclipsed Moon from a bright city road? (May 26, 2021 total lunar eclipse)

texts:
Due to scheduling and geometry I could only snap last night's lunar eclipse with an older model cell phone on a pedestrian overpass of a brightly lit city street, but surprisingly the Moon was quite bright even during the totality phase (U2 to U3 (14.5 minutes) also see below) when the Moon was within the geometrical umbra of Earth's shadow.
   2021-05-26
----------------
U1 = 09:44:57 UT     first contact with umbra
U2 = 11:11:25 UT     begin totatity
U3 = 11:25:55 UT     end totality
U4 = 12:52:22 UT     last contact with umbra

This eclipse just barely grazed the inside of the umbra.
The last total lunar eclipse I remember was quite a long time ago. It was more central and the Moon barely visible with night adapted eyes viewed from the countryside, so it's not a fair comparison.
But I'd like to ask anyway:
Question: Was the radial gradient of Earth's umbra unusually bright for the May 26, 2021 total lunar eclipse? Might there have been more light scattered from Earth's atmosphere into the umbra than average, due to weather or perhaps the recent eruption Mount Nyiragongo in the Democratic Republic of Congo? Or was the brightness of the northern edge of the Moon pretty much normal for this geometry?

above: Snapshot at 2021-05-26 11:23:58 UTC North is left (altered only to obscure a phone number on a sign)
below: from eclipse.gsfc.nasa.gov's Total Lunar Eclipse of 2021 May 26 found here. North is up


texts: Galactic Filaments and their connection to Galaxy centre

texts: If alliptical galaxies seem to a line with their associated galactic filament and that orientation is related to connections between the mass of said galaxy and the dominating central object, which evolves that orientation. Is there a relation between these filaments and the supermassive central object as a start or destination point?


texts: Are there collected data about the direction of rotation of black holes and the direction of the magnetic field?

texts:
Is there a relation between the direction of rotation of black holes or neutron stars and the magnetic dipole moment of BH or neutron stars? BTW, are there different directions of this two parameters for suns?

Edit

I want to be sure there are or there are not the direction of rotation (which one can expressed by an arrow on the rotation axis) and the direction of the magnetic field (expressed by an arrow from the south to the north pole (both arrows are simple conventions)) parallel only. I'm not sure that the direction of the magnetic field is observable at all. And the comment from Zibadawa Timmy about pulsars perhaps a good extension to my question about BH, neutron stars and Suns.


texts: I've seen websites that show the ratios of the 10 most common elements but they compare them by relative mass. I think it's more interesting to know the relative abundances of atomic nuclei because that is what you need to know to understand why the universe has the chemical makeup that it does. What are the 10 most abundant elements in the universe by number of atomic nuclei?


texts:
Rosetta Comet AKA 67P/Churyumov–Gerasimenko has the surface temperature range of -43 to -93 degree Celsius.

Now, if we compare that with the Mercury (I chose Mercury cause it's closest to the Sun and has the thinnest atmosphere), the minimum surface temperature is -170 degrees Celsius. A little farther from that, on Earth's Moon, while at night, the temperature can drop up to -233 degree Celsius.

Rosetta's Comet is farther from the Sun as compared to both objects (Perihelion 1.2432 AU, Aphelion 5.6829 AU); however, a lot warmer. Why is that?


texts: Black holes from my knowledge are created from the collapse of a star’s own gravity crushing itself, Now my question is well two questions, is it really infinitely dense to where space-time can be distorted to the point where it just stops? if so, this would mean objects caught in the event horizon would freeze and time would be stopped how is the black hole itself not effected by it’s own mass wouldn’t it just cease to exist in the first place?


texts: What to look for in a tripod for binoculars?

texts:
I have been looking at large astronomy binoculars in the 25x100 and 20x80 range. Clearly, these monsters cannot be held steady by hand, or even be held at all for any reasonable length of time using one's arms.

Somewhat related question What should I look for in an astronomy tripod? isn't helpful as a telescope tripod needs to hold a much bigger weight, so it stands to reason that one would get away with something lighter and cheaper for big binoculars.

What's recommended, tripod-wise? Any related pro tips from the binocular crowd?


texts: Can tidal locking increase rotational kinetic energy? Where does the energy come from then?

texts:
I was thinking about the explanation for how the Moon gets tidally locked with the Earth. We are working in the non-rotating reference frame of the Earth, and assume it is inertial (to an approximate degree). I was looking at the explanation given in this link (see 2nd and 3rd paragraphs).
Because tidal forces of gravitation cause bulges of the moon (in the direction of the Earth-Moon axis), any rotation of the Moon that does not match the orbit of the Moon around Earth will lead to a torque on the Moon, causing the rotation period to gradually become closer to the orbital period.
If the Moon rotates too fast, the usual explanation tell us that the rotational kinetic energy dissipates into heat via tidal friction. This makes complete sense. However, there seems to be an obvious follow-up question to this: What if the rotation of the Moon is too little? Where does the energy come from?
I can see how rotational kinetic energy of the Moon is dissipated into heat by tidal forces, but I don't understand where the energy comes from in the case where the Moon is rotating too slowly (from the point-of-view of Earth non-rotating reference frame). Is tidal friction the right terminology here?
If there are any answers, are there any calculations to support them?


texts: Does a flat universe mean not finite and circular?

texts:
I am trying to wrap my head around what a flat universe means; Trying to imagine why angles of triangles in spherical volumes are different.

Because my brain can't do that well and I became a bit annoyed by it, I started to think about a hypothetical circular one dimensional universe (a circle) - placing myself on the circle.

Without access to a "detached" view from the second dimension, just being able to look back and forward, I don't see any possible way to determine whether my universe is circular or not - apart of seeing my own back - if light already traveled around the whole circle.

So, thinking about two dimensions (a sphere, I guess), I still can't imagine to see any kind of circle, curvature or special angle, because I imagine the curves would lift into a "detached" third dimension which is not there from my point of view?

I don't understand how one would see curvature without access to a detached view of the higher dimension, could someone relieve me from this headache? - Does a flat universe actually mean that it is non-circular?


texts:
We know that the visual size of the Sun and Moon from the Earth in our lifetime (!) is nearly equivalent.
Now my question: Is this event is random? Or have a scientific reason?
For example, maybe there is a connection between this and the formation of life on the Earth...


texts: What are the differences between a Black Hole and a Supermassive Black Hole

texts:
From what I understand, the mass of a black hole should be nearly infinite, how much more massive can something get?

Is the name to be literally interpreted such that a Supermassive Black Hole just has more mass?
Or rather, is a Supermassive Black Hole just a regular Black Hole with nearly infinite mass that is larger in diameter?
If the difference is in fact a change in diameter, how are the changes in size with the retention of the immense mass reflected in the Supermassive Black Hole's gravitational field?


texts: What do we know about the relation of shape to size in asteroids?

texts: Have enough good measurements been made of small asteroids to gather interesting statistics about roundness?  Perhaps a scatter chart of each body's greatest and least diameter?


texts: Concerning the "Lithium test" for Brown Dwarfs

texts:
Both low-mass PMS (pre-main-sequence) stars and young brown dwarfs can fuse lithium in their cores and the lithium can be depleted throughout the star/brown dwarf very quickly. Wiki. Then the Li I 6708A absorption line disappears from the object's spectrum.

Why and how can the Lithium test be used as an indicator to distinguish between young brown dwarfs and young low-mass stars?

Can somebody summarise in what cases we can tell whether an object is a brown dwarf or a low-mass star?


texts: What is the size of the largest asteroid orbiting the Earth, other than the Moon?

texts: It seems odd to me that no other asteroid around the Earth is even close to the size of the Moon. Anyone have any idea about the size and orbit radius of Earth's "second moon" ?


texts: Are red dwarfs (M dwarfs) known to be strong infrared sources?

texts: If so, why? Are they known to be surrounded by large amounts of dust? Do they typically flare?


texts: How close would merging black holes have to be to feel gravitational waves?

texts:
Recently LIGO discovered gravitational waves caused by two black holes that were orbiting each other, and then collapsed into one black hole. A few months later, we find out that this actually happens quite often. However, these collisions are far enough away from Earth that no one can feel the gravitational waves, and it actually takes very precise measurement to even determine that they happen. So my question is, how close would a black hole collision have to be for us to feel the gravitational waves pass through Earth?

Secondly, is this even possible? As in, would the distance have to be so short that we'd get swallowed up before the black holes collided? And, if we were to feel such gravitational waves, what would they feel like?

EDIT: Let's say that the black holes have the same mass as Earth, giving their event horizons a radius of about 9 mm (the size of a dime). So two Earth-sized black holes that are stuck in an orbit finally collapse is the scenario here.


texts: What is tilt anisoplanatism for Laser-guide-star usage in adaptive optic systems?

texts: How does tip-tilt mirrors correct such issue? What is the physical origin of the error?


texts: Is it difficult to see DSO in your eyepiece?

texts: I want to know if bringing the image of a DSO in eyepiece generally represents a problem for beginners in astronomy.


texts: Does the Milky Way orbit around anything?

texts:
We know most of the objects in the Universe have a spherical or elliptical shape. The object which has less mass and gravitational pull orbits around the nearest object with more mass and gravitational pull. For example:

Moon orbits around Earth
Earth orbits around Sun
Sun orbits around Sagittarius A* which is the center of Milky Way.

Thus, is the Milky Way orbiting around some object or perhaps Black Hole?

I know that the Milky Way is going towards Andromeda as they are attracting each other and they will collide with each other after 3 billion years to 6 billion years. But it is possible that the Milky way is orbiting around some object at the same time? Perhaps both galaxies are present in a group of galaxies which is orbiting around some object.

If the Milky Way is not orbiting around some object then is there any proof found by the scientists for that?


texts: Is it possible for a virus to come from a meteorite?

texts:
So I am not a true scientist and I was just wondering if an extraterrestrial rock from space can have some dangerous unidentified virus or bacteria that can be deadly and wipe out the Earth if it not quarantined. Is this science fiction?.

P.S.: Note I said extraterrestrial rocks not extraterrestrial as in aliens.


texts: Why was Pluto's resonance not discovered until 1965?

texts:
Over here, I was shocked to learn:

  The Neptune–Pluto system lies in a 3:2 orbital resonance. C.J. Cohen and E.C. Hubbard at the Naval Surface Warfare Center Dahlgren Division discovered this in 1965.

Note: there is no cite for it.

I'm pretty sure the orbit of Pluto, including it's period, was calculated many years before 1965, to say nothing of Neptune. So how is it possible that astronomers missed the 2:3 resonance? Was orbital resonance just not a conceived concept until the sixties?


texts: What characteristics or patterns do galaxies have on color-luminosity chart?

texts:
For the following graph, I have some confusions:

How do galaxies rank by mass? We know that on main-sequence, more luminous stars are also more massive, so I guess it also applies to galaxies.
Do red sequence galaxies split into blue galaxies, or do blue galaxies merge into bigger red galaxies?
Can galaxies ever be born as red sequence members? I doubt it because all galaxies should start from blue. But I am not 100% sure.
Do red sequence galaxies tend to become redder over time?
Do large galaxies use up star forming gas more rapidly than smaller galaxies?


texts: Why do pair production and photodisintegration have such different effects in collapsing supermassive stars?

texts:
Stars of at least 100 solar masses or so can reach core temperatures (and, thus, core photon energies) great enough that pair production (where a very-high-energy photon strikes another particle, transforming the photon into a matched particle-antiparticle pair - usually an electron-positron pair, though other types are possible - and causing the other particle to recoil slightly) starts to occur in earnest.  As this is an endothermic (energy-absorbing) process, it reduces the temperature and pressure within the star’s core, causing the star to start to collapse under its own weight.

One of three things can now happen:

In high-metallicity stars, and in low-metallicity stars up to ~130 MS, the resultant increase in core temperature and pressure halts the collapse before it can do anything irrevocable, and the star heats up and expands back out again, blowing off significant mass in the process.  These pulsations will continue until either the star becomes too small and cold for much pair production or it explodes for some other reason.
In low-metallicity stars from ~130 to ~250 MS, the collapse compresses and heats the interior of the star quickly and vigorously enough that the resulting increase in core reaction rate and energy release is sufficient to unbind the entire star.
In low-metallicity stars exceeding ~250 MS, the collapse is so rapid, and the rise in core temperature so great, that an increasingly-large fraction of the photons produced have energies high enough to cause photodisintegration (where an extremely-high-energy photon is absorbed by an atomic nucleus, causing the nucleus to break apart into two or more smaller pieces), robbing the star’s core of energy and causing the entire star to collapse directly into a black hole.

Both pair production and photodisintegration are endothermic (energy-absorbing) processes, and, thus, tend to cause the star to collapse.  However, their eventual effects on the collapsing star are different; pair production causes only a partial collapse, followed by runaway thermonuclear fusion and a supernova explosion, while photodisintegration causes a complete collapse into a black hole, with nothing escaping.

Why does core energy loss resulting from pair production result in a partial collapse, runaway fusion, and a supernova, while core energy loss resulting from photodisintegration results in a complete collapse to a black hole?  Why don’t these two endothermic processes either both result in a partial collapse with resulting explosive fusion, or both result in total collapse to a black hole?


texts: Observable universe equals its Schwarzschild radius (event horizon)?

texts:
The estimated age of the universe is 14 billion years.

The estimated Schwarzschild radius (event horizon) of the observable universe is 14 billion light-years.

What are the ramifications?


texts: Why does the neutral hydrogen velocity have this characteristic behavior in the galactic plane?

texts:
The recently released map of galactic neutral hydrogen density and velocity is really beautiful. The work has been relased by the HI4PI collaboration (HI = neutral hydrogen, $4\pi$ = complete spherical coverage).

My question is fairly simple. Looking at the image near the galactic plane, why do I see near the center a green bump on the left and a blue bump on the right, then near the edges of the image a much stronger blue bump on the left and a green bump on the right. In other words, there is a major and a minor peak in the positive radial velocity gas, and a major and a minor peak in the negative radial velocity gas.

Does this have some simple geometrical explanation?

above x2: neutral hydrogen density/velocity map from here with inset indicating color scale expanded.

above: for those who can not distinguish the green and blue in the image, this plots the average green (solid) and blue (dashed) intensity within the central equatorial band.

There is a nice article at phys.org with a video, which can also be seen in YouTube. It shows the intensity of HI as a cut in radial velocity is slowly scanned through the data set.

https://www.youtube.com/watch?v=Q2mgpsTFuV8

Since the stackexchange YouTube option is not turned on in astronomy stackexchange, here is a GIF of screenshots at -30, -20, -10, 0, 10, 20, and 30 km/sec:


texts: What star was the asteroid 2014 MU69 predicted to occult on 2018-08-04?

texts:
From a search, I found a list of some preparatory HST observations made for the August 4, 2018 occultation of a star by the asteroid 2014 MU69

  We propose observations in support of the upcoming New Horizons encounter for 2014MU69. One visit is for support observations of a star to be occulted by 2014MU69 on 2018 August 4 from which ultra-precise astrometry and shape information about the target can be derived. The second visit is for a backup epoch of astrometry on 2014MU69 itself at the end of the 2018 observing window at a time when New Horizons will also be observing the target. (minor typographical edits made)

Five lines are shown, for measurements between 2018-04-30 01:03 and 01:48. The target is listed as MU20180804 but that name seems to be the identification of an occultation, not the name of a star.

So far I have not figured out the actual identity of the star that was predicted to be occulted by 2014 MU69 on 2018-08-04.

Here is a very nice prediction for three occultations by 2014 MU69 last year (2017). However when I go to the main page for that asteroid occultation site and look at 2018-08-04 I don't see any events with MU69 as the asteroid!

See also Will the upcoming observations of occultation by “Ultima Thule” (2014 MU69) be of a single object, or two?


texts: How does space time differ within a galaxy?

texts:
Not the same question but is similar to other marked duplicate.
How much time dilation  does the center of a galaxy can exist and sustain human life from our point of view? What would a day equal to each others point of view looking at each other?

I'm not asking about moving celestial bodies moving from each other but the difference in the gravity wells from the center of our galaxy being generally denser then the edge of a galaxy.

This is another way of asking if I wasn't clear above the line. Not to invalidate any answers.

Point 1 being near the center of the galaxy and point 2 at the the most edge the galaxy. How much would the differences in the galaxies gravity well point 1 being deeper in the center compared to the point 2 the edge effect time?


texts: Could our Sun be the product of an ancient stellar collision?

texts: The canonical model for the formation of the Solar System involves the gravitational collapse of a nebula into (perhaps) several stars across several light years. Is it possible that two or more of the stars (or protostars) combined to form our Sun?  Or would any stellar collision release so much energy that our Sun could not have formed the way we see it today?  Have astronomers or astrophysicists created n-body orbital models that allow for a "soft" collision of two stars combined with the ejection of the other(s)?


texts: What causes the raise of temperature in the outer layer of a red giant when the core gets contracted?

texts:
A star emits energy through the fusion of hydrogen to helium in the core through the proton proton cycle or the carbon nitrogen cycle. Over time, hydrogen in the core is increasingly burned, which causes the fusion process to decrease over time. As a result, the star cools down and decreases the radiation pressure in the core. As a result, the core draws a little more together under the influence of its own weight, which increases the temperature. This temperature rise leads to a hydrogen fusion in a shell outside the core.

But how is the temperature increased as the radiation pressure is decreased? Is this increase caused by conduction or convection or....?


texts: Is every single large solid body orbiting entirely outside of the frost line covered in ice?

texts: Not sure where I heard that but I want to make sure if it's true. Forget about the asteroid belt for a minute: Are all the moons of the outer planets and kuiper belt objects covered in water ice?


texts: Why do we only have one major meteor shower from 3200 Phaethon?

texts:
When talking to my son about the Geminid meteor shower tonight, we read up on 3200 Phaethon, and were curious: why is there only one meteor shower from 3200 Phaethon, and not two?  Given its orbit, the Earth crosses the sunward orbit of 3200 Phaethon in December, and the after-sun orbit the next September or October (see this orbital diagram on wikipedia for example.)
Why does only the one side of the orbit have a major meteor shower, and not the other (as far as I know, anyway)?  This seems true for any of the major showers - Swift-Tuttle also crosses our orbit twice as well, of course, once in (northern hemisphere) spring and once in August, as must any other comet (assuming none are perfect tangents to our orbit, which seems unlikely).  Why does only one side of the orbit cause a meteor shower?
And, why it is it not always the same side of its orbit - 3200 Phaethon causes the shower heading towards the sun, while Swift-Tuttle causes the Perseid shower after it's past the Sun and is headed back out?  (I'd thought perhaps the shower was caused by debris from the sun approach at first, but of course that mustn't be the case if I read the orbital diagram properly; and then later I thought that maybe the Sun vacuumed up the debris, but then Swift-Tuttle has the opposite result.)
Is it simply orbits in three dimensions (and the comet/asteroid coincidentally crosses Earth's orbit once on Earth's orbital plane, but the other crossing is on a different plane)?  Would both sides of the orbit produce similar effects, if the comet was in precisely the same plane as Earth?  Or are there "dusty" and "clean" portions of the asteroid's/comet's orbits?


texts: Polar satellites for Global Navigation Systems

texts: Why do we need 7 polar satellites for a navigation system like the Indian Regional Navigation Satellite System (IRNSS)?


texts: How does inflation justify the nonexistence of magnetic monopoles?

texts: It is said that inflation justifies that magnetic monopoles don't exist. Can anyone explain how inflation theory explains the non existence of magnetic monopoles?


texts:
I've read that even light cannot escape from black holes.
The speed of light is theoretically predicted to be the escape velocity of a black hole.
I've also read that the general notion that nothing can escape from a black hole is wrong.  Even black holes emit particles and radiation known as the Hawking radiation.
My question is: How can black holes emit any kind of radiation?
If they even do emit, wouldn't the speed of the radiation be less than or equal to velocity of light?
If the escape velocity of a black hole is c, then how can the Hawking radiation even escape the black hole? Wouldn't it be pulled back into the black hole? Then, how is it even
emitting anything?


texts: Textbook to explain measurements and calculations for heliocentric solar system

texts:
I'm trying to identify a textbook I had briefly and then lost. I had a PDF file of an astronomy textbook, but the hard drive crashed irreparably before I could thoroughly read the textbook, or even record the author and title.

The textbook covered the history of geocentric theories, explained how to make basic astronomical instruments to measure angles, and how to make arguments for heliocentrism. As I recall, the book mentioned that given high-resolution photography, one can prove heliocentrism by measuring how some celestial bodies appear larger at different times of the year.

I am trying to at least work through the calculations for heliocentrism on paper, even if I don't end up crafting my own instruments. If no one knows of any one textbook that covers all these topics, I would still be grateful for relevant textbooks that cover some of these topics.

Update: It is not a complete answer, but a good start can be found with the ephemeris question asked at:

https://astronomy.stackexchange.com/a/7973/29149


texts: Could there be a closer star to Earth than the Alpha Centauri triple star system, excluding the Sun?

texts: Do we know for certain that the nearest star to Earth, excluding the Sun and the theorized Nemesis, is the Alpha Centauri multiple star system, at +/-4.4 light-years away? Have we been able to identify every star that is <5 light-years from Earth or is there a possibilty a faint star could be nearer?  Are there stars that we haven't looked at yet that could be closer?


texts: Is there a planet or planetary moon flyby path that could send a solar prograde orbiting asteroid into a retrograde solar orbit?


texts: Is there a connection between black holes and dark matter/energy?

texts: Is there a spatial or gravitational relationship between black holes and dark matter/energy?


texts: Given a fixed coordinate location on Earth (i.e. a latitude and longitude), and a fixed equatorial coordinate location of a particular astronomical object in the sky (i.e. right ascension and declination), how can I calculate the horizontal coordinates as a function of date and time on Earth?